Firstly, population density: which areas had the most people?
Density is calculated as the number of people per hectare, and
we have measured areas from a modern digital map of the local
authorities rather than relying on the doubtful acreages given in
historical reports.
Secondly, growth rates: where was population rising fastest,
or declining? We also look at the ratio of men to women.

This theme also covers people's ages.
From 1851 onwards, the census has provided very detailed statistics
of age structure, giving numbers of males and of females in each 5-year age band.
However, we simplify this here to three broad age groups:
Children (0-14), Working Age (15-64) and the Elderly (over 65).

Over the last 150 years, our population has clearly aged.
However, mortality decline in the late 19th century was mainly due to the
reduction of very high infant mortality rates:
the presence or absence of large number of infants dying before their first
birthday had little effect on overall age structures.
During the twentieth century, declining fertility and improved life expectancy
in later life significantly changed age structures.

We hold these detailed statistics for Derbyshire, which we graph
and tabulate here: